解释这个正则表达式js

Question

我正在使用这个正则表达式匹配一些字符串：

^([^\s](-)?(\d+)?(\.)?(\d+)?)$/

我很困惑为什么允许输入两个点，例如..

据我所知，只允许放1个破折号或{1}} 没有限制或没有(-)?的任何数字 一个点或没有(\d+)?

为什么允许放置(\.)?甚至..？

在http://www.regextester.com/

中完成测试

Answer 1

[^\s]表示任何不是空白的内容。这包括点。尝试匹配..会让你：

1. [^\s]匹配.
2. (-)?不匹配
3. (\d+)?不匹配
4. (\.)?匹配.
5. (\d+)?不匹配
<小时/> 我假设你想匹配数字（可能是负数/浮点数）：

^-?\d+(\.\d+)?$

Answer 2

^([^\s](-)?(\d+)?(\.)?(\d+)?)$/

• Assert position at the beginning of the string ^
• Match the regex below and capture its match into backreference number 1 ([^\s](-)?(\d+)?(\.)?(\d+)?)
  • Match any single character that is NOT present in the list below and that is NOT a line break character (line feed) [^\s]
    • A single character from the list “\s” (case sensitive) \s
  • Match the regex below and capture its match into backreference number 2 (-)?
    • Between zero and one times, as few or as many times as needed to find the longest match in combination with the other quantifiers or alternatives ?
    • Match the character “-” literally -
  • Match the regex below and capture its match into backreference number 3 (\d+)?
    • Between zero and one times, as few or as many times as needed to find the longest match in combination with the other quantifiers or alternatives ?
    • MySQL does not support any shorthand character classes \d+
      • Between one and unlimited times, as few or as many times as needed to find the longest match in combination with the other quantifiers or alternatives +
  • Match the regex below and capture its match into backreference number 4 (\.)?
    • Between zero and one times, as few or as many times as needed to find the longest match in combination with the other quantifiers or alternatives ?
    • Match the character “.” literally \.
  • Match the regex below and capture its match into backreference number 5 (\d+)?
    • Between zero and one times, as few or as many times as needed to find the longest match in combination with the other quantifiers or alternatives ?
    • MySQL does not support any shorthand character classes \d+
      • Between one and unlimited times, as few or as many times as needed to find the longest match in combination with the other quantifiers or alternatives +
• Assert position at the very end of the string $
• Match the character “/” literally /

使用RegexBuddy

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Answer 3

正如我在评论中提到的， [^\n]是一个与. 匹配的否定字符类。并且由于还有另一个(\.)?模式，正则表达式可以匹配2个连续的点（因为[^\s]以外的所有部分都是可选的。）

为了不匹配.4.5或..等字符串，您只需将.添加到[^\n]否定字符类：

^([^\s.](-)?(\d+)?(\.)?(\d+)?)$
      ^

见demo。这不会让初始捕获组中的任何.。

您可以使用前瞻只将第一个字符禁止为点：

^(?!\.)([^\s](-)?(\d+)?(\.)?(\d+)?)$

请参阅another demo

所有解释均可在在线正则表达式测试人员处获得：

为了匹配您期望的格式的数字，请使用：

^(?:[-]?\d+\.?\d*|-)$

人类可读的解释：

• ^ - 字符串的开头，然后有2个替代方案......
• [-]? - 可选连字符
• \d+ - 一位或多位
• \.? - 可选点
• \d* - 0位或以上
• | - 或 -
• - - 连字符
• $ - 字符串结尾

请参阅demo